Galvanic cells may generate large quantities of gas under certain conditions during use. Since many such cells are required to be tightly sealed in order to prevent loss of electrolyte by leakage, high internal gas pressures may develop. Such pressures may cause leakage, bulging or possible rupture of the cell's container under abusive conditions if not properly vented.
In the past, several different types of resealable pressure relief vent valves have been used for releasing high internal gas pressures from inside a sealed galvanic cell. One type of valve that has been commonly used consists basically of a valve member such as a flat rubber gasket which is biased into sealing position over a vent orifice by means of a resilient member such as a helical spring. The resilient member or spring is designed to yield at a certain predetermined internal gas pressure so as to momentarily break the seal and allow the gas to escape through the vent orifice.
With the continuing development of portable electrically powered devices such as tape recorders and playback machines, radio transmitters and receivers, and the like, new types of reliable, long service life cells or batteries have been developed. These newly developed electrochemical cell systems provide a long service life by utilizing highly reactive anode materials such as lithium, sodium and the like, in conjunction with high energy density cathode materials.
U.S. Pat. No. 4,400,453 discloses a nonaqueous electrochemical cell comprising an anode, a cathode collector and a cathode-electrolyte, said cathode-electrolyte comprising a solution of an ionically conductive solute dissolved in an active cathode depolarizer wherein said active cathode depolarizer comprises a liquid oxyhalide of an element of Group V or Group VI of the Periodic Table. The "Periodic Table" is the Periodic Table of Elements as set forth on the inside back cover of the Handbook of Chemistry and Physics, 63rd Edition, The CRC Press, Inc., Boca Raton, Fla., 1982-1983. For example, such nonaqueous cathode materials would include sulfuryl chloride, thionyl chloride, phosphorus oxychloride, thionyl bromide, chromyl chloride, vanadyl tribromide, chromyl chloride, vanadyl tribromide and selenium oxychloride.
Another class of liquid cathode materials would be the halides of an element of Group IV to Group VI of the Periodic Table. For example, such nonaqueous cathode materials would include sulfur monochloride, sulfur monobromide, selenium tetrafluoride, selenium monobromide, thiophosphoryl chloride, thiophosphoryl bromide, vanadium pentafluoride, lead tetrachloride, titanium tetrachloride, tin bromide trichloride, tin dibromide dichloride and tin tribromide chloride.
One possible disadvantage in the use of oxyhalide and halide liquid cathode nonaqueous cells is that it may be possible that, during storage or use, some of the oxyhalide, halide or their reaction products may escape from the cell. This escape of liquids and/or gases could cause damage to the device employing the cell or to the surface of a compartment or shelf where the cell is stored. On the other hand, if the seal of the cell is effectively permanently secured, then it is possible that the build-up of internal pressure within the cell could cause the cell's container to rupture which may cause property and/or bodily damage. To prevent rupture of the cell's container from possible internal pressure build-up caused under abusive conditions, such as charging and exposure to a high temperature environment, it is necessary to vent the cell at some predetermined pressure.
To overcome the potential problem of leakage of liquid cell components between the vent orifice and the member closing the vent orifice, U.S. Pat. No. 4,529,673, discloses the use of a corrosion-resistant material disposed at the interface of the wall defining a vent orifice and a force-fitted member. However, during storage and discharge, some electrolyte may at times leak at the interface of the wall defining the vent orifice and the corrosion-resistant material.
U.S. Pat. No. 4,931,368 discloses an electrochemical cell having a cell housing having a vent liner containment section that comprises a sealing well having a bottom disposed toward the interior of the cell, an orifice in the sealing well and a support ledge at the bottom of the sealing well; a vent liner having a vent liner orifice disposed within the sealing well so that an end of the vent liner abuts the support ledge, the orifice in the sealing well and the vent liner orifice providing a path from the interior of the cell to the atmosphere; and a seal member force-fitted within the vent liner, wherein the vent liner and the seal member are adapted so that the seal member will be at least partially expelled from the vent orifice at a predetermined internal gas pressure within the cell.
In U.S. Pat. No. 4,592,970 a cell is disclosed that is similar to the cell in U.S. Pat. No. 4,529,673 except that a sealant is disposed at the interface of the wall defining the vent orifice and the liner so as to prevent any electrolyte from leaking at the interface of these components.
U.S. Pat. No. 4,855,195 discloses an electrochemical cell comprising (a) an electrode assembly containing a positive and negative electrode; (b) a housing containing the electrode assembly, and containing a means for providing a terminal for one of the electrodes; (c) a cover assembly containing a means for providing a terminal opposite the terminal of the housing to thereby establish an electrical circuit in the cell; and (d) a current collector member disposed in the circuit and in physical contact with one of the electrodes; said collector comprised of a shape-memory alloy, and having a base portion and a plurality of legs extending from the base portion; wherein the collector provides a means for disconnecting the electrical circuit in the cell when the internal temperature of the cell rises.
U.S. Pat. No. 4,529,675 discloses a rechargeable electrochemical cell comprising: a sealed cylindrical container having first and second ends; an electrode assembly disposed in said container and spirally would about an axis, said assembly comprising first and second electrodes with a separator disposed therebetween, said first electrode having an offset edge segment extending at said first end in a first axial direction axially beyond said second electrode; an electrolyte disposed within said container and infiltrating said first and second electrodes and said separator; a current collector disposed in said container axially adjacent said offset segment of said first electrode, said collector having a base portion spaced from said offset segment and in electrically conductive contact with said container, said collector further having a plurality of deflectable tabs each projecting from said base portion and into electrical contact with said offset segment at a plurality of locations along said offset segment, said tabs being in a deflected condition to exert a contact force on said offset segment and thereby effect electrical conductive engagement between said tabs and said offset segment at each of said locations.
It is, therefore, an important object of this invention to provide a spring contact means for a safety vent closure for electrochemical cells that will vent at a predictable low pressure and not before.
It is another object of this invention to provide a spring contact means for a safety vent closure for cylindrical cells employing, for example, liquid oxyhalides and solid cathode materials such as FeS.sub.2 or MnO.sub.2, as the active cathodic material.
It is another object of this invention to provide a spring contact means for a safety non-resealable vent closure for nonaqueous cells that is inexpensive to manufacture and easy to assemble.
The foregoing and additional objects will become fully apparent from the following description and the accompanying drawings.